Round and non-round paper containers have achieved considerable popularity for the packaging of a variety of products, especially food products. Conventional practice in the manufacture of non-round paper containers involves wrapping flat paper side wall blanks around mandrels having a desired non-round cross-section and heat sealing edge portions of the blanks together to form an overlapped seam. A bottom disk is then applied and the bottom edge portion of the container body is crimped onto and sealed to the disk. The top edge of the container is usually curled or rolled for strength and for receiving a removable lid.
The machinery that has been developed in the past to carry out these operations has been satisfactory for the most part, however, it has not been wholly free of problems. Existing machines are not able to produce enough containers to meet the 1800 gallon per hour freezer capacity which is common in the ice cream industry. Consequently, it is necessary to use more than one machine to meet the prevailing standard of freezer capacity. Another problem is that the faster machines are expensive and thus disadvantageous for relatively low volume operations where the volume is insufficient to justify the expense. Existing machinery is further characterized by an inability to be adjusted easily to handle containers that vary in shape, diameter and/or height.
The container side wall blank must be wrapped closely around the mandrel or its shape can vary to an unacceptable extent. In the past, wrapping has been carried out in a wholly mechanical fashion, and the side wall blank can exhibit crinkles or other deformities that make the container defective. It has also been difficult to achieve uniform heating of the edge portions of the blanks in order to assure a strong and effective seam on the side wall of the container.
Applicant has proposed a conventional system (U.S. patent application Ser. No. 07/854,319, entitled "Machine and Method For Forming Round Paper Containers" which was filed Mar. 19, 1992 and abandoned on Mar. 11, 1993 incorporated herein by reference) in which flat paper side wall blanks are held on edge in a stack in a magazine. A pusher arrangement holds the front or leading side wall blank in position to be picked up by suction cups which are carried on a rotary turret. When the turret rotates to position a pair of the suction cups in front of the leading blank, the suction cups are extended and suction is applied to them so that the blank is picked off of the stack when the cups are retracted.
The turret then rotates by an incremental arc of 90 degrees, and the suction cups carry the blank along curved rails which maintain the blank in a curved configuration when it stops at a heating station located at the top of the turret. A pair of curved heaters apply heat to the opposite edges of the blank to melt resin with which the paper blank has been treated. The turret is rotated by another 90 degree increment to carry the blank to a wrapping station. At the wrapping station, the suction is relieved on the suction cups and a linear clamp rotatably drives vertical slides along a track to push the blank against a mandrel. Thereafter, separate vertical rods are rotatably driven about a mandrel along an arcuate path to wrap the blank around the mandrel. Vacuum applied to circumferential grooves in the outer surface of the mandrel assures that the blank closely conforms with the mandrel surface before the overlapping edges are sealed by a pressure bar.
The vacuum is applied to the interior of the mandrel and through ports to the vacuum channels or grooves in the mandrel surface. The ports are located on the front of the mandrel which is the part of the mandrel that is first contacted by the blank. Consequently, the ports are immediately covered by the blank and the vacuum force is able to follow the grooves as the blank is progressively wrapped around the mandrel.
Pivotal wrapping wings carry the vertical rods that actually wrap the blank as the wings are pivoted. A unique rack and pinion mechanism causes the wings to travel at different speeds so that the two wings finish their movement at different times. This creates an overlap in the edges of the side wall blank and assures an overlapping seam. The curvature of the blank while it is being heated provides it with a strong, stable shape and assures that the heating takes place uniformly to provide a consistent seam along the height of the container wall. The suction cups in each pair are adjusted in and out to accommodate containers which differ in diameter. The magazine is adjustable up and down to provide the machine with the ability to easily handle containers that vary widely in both diameter and height.
However, even the foregoing system proposed by the applicant experienced certain limitations. In particular, applicant's foregoing system was primarily intended for use with round paper containers having a uniformly curved contour. The round containers also had a large radius with a slightly curved surface upon which the overlapping seam was formed. This system was ill suited for non-round containers.
Heretofore, machines for producing non-round paper containers have experienced at least three primary disadvantages, namely a complex and space consuming mechanism for wrapping the container blank about the non-round mandrel, a complex and expensive mechanism for extracting a completed container from the machine and an inability to produce smooth seams upon non-round containers having a substantially small radius at the seam. For instance, the pivotal wrapping arms of applicant's conventional system were ineffective with multiple container sizes and were unable to cause the blank to conform to the mandrel. As to the extraction mechanism, the conventional systems removed a container from the mandrel by physically grabbing a rim formed about the bottom edge of the container. Once this edge was grasped, the container was pulled downward off of the bottom of the mandrel. However, this process required additional machinery both to form the lower lip and to effect extraction.
Applicant's conventional system eliminated this lower lip and the mechanism necessary to construct and grasp such a lip in a round container application. Applicant's conventional round system utilized the plurality of air grooves about the mandrel to remove the container. Once a container was completed, air was blown outward through these grooves, thereby causing round containers to swell uniformly and to separate from the mandrel to effect self-release. Thereafter, gravity and air caused the container to fall off the bottom of the mandrel. The machine for producing round containers afforded self-release since the containers offered a uniform curvature and thus the expelled air acted uniformly upon the container.
However, air expelled outward through the mandrel does not react uniformly upon a non-round container. Instead, the air focuses upon the substantially flat portions of the container and has little effect upon the more arcuate portions thereof. By focusing air in this manner, the substantially flat portions of the container swell outward, thereby causing the end arcuate portions to pinch against the mandrel and bind. Once these end portions bind, the container will not self-release from the manual. Hence, forced air is ineffective as a means to release non-round containers from the container producing machine.
Moreover, conventional systems have been unsuccessful in forming smooth seams along the adjoining edges of a non-round containers having certain contours. This problem is due substantially to the fact that seams upon non-round containers are typically provided along end portions of the containers having a somewhat small radius of curvature. Wrinkled seams are created along the container ends since, prior to introduction of the side seam clamp, the overlapping edges of the wall blank do not conform to the mandrel at the seam, but instead project outward therefrom (at a tangent to the mandrel) to form a V-shaped intersection with one another.
More specifically, when a non-round container is formed, the mandrel is oriented with its opposite ends having the shorter radius and the sides having the larger radius. In the past, the seam has been formed along one of these ends. Along this line, the conventional machine contacted the forward most portions of the container blank to cause such edge portions to overlap the end of the mandrel. However, the wrapping mechanism in these machines was unable to directly contact the outermost ends of the container blank as it would interfere with the sealing mechanism. The sealing mechanism requires a free zone which could not be interfered with by the wrapping arms. Within this free zone, the outermost ends of the wall blank remain straight and projected tangentially along the mandrel. These tangential portions of the container blank intersect to form the V-shaped bridge which the sealing mechanism attempts to collapse against the mandrel. These outer ends are covered with a hot poly resin and, once heated in the heating station, do not effectively slide against and collapse upon one another to lay flush against the end of the mandrel. Instead, the hot poly resin upon each end sticks to one another prematurely thereby causing a wrinkle at the seam.
It is the object of the present invention to overcome the problems experienced heretofore.